1. Modify the specification discussed in this section by introducing the elevator's door and the operations that open and close the door, respectively. 2. Modify the specification of the elevator, assuming that the elevator moves continuously from the first to the last floor and back, instead of responding to the internal and external requests of users. 3. Consider the following specification of a change command for a word processor: Is this specification formal or informal? Is it operational or descriptive? Is it ambiguous?